Manipulation of fluid objects using acoustic radiation pressure: Beyond drops and bubbles and retrospection

Abstract

Some standard applications of acoustic radiation pressure include the manipulation of drops and bubbles for the study of interfacial dynamics and light scattering. After a review, this presentation summarizes recent applications including radiation pressure effects on small flames and liquid cylinders [Wei et al., J. Acoust. Soc. Am. 116, 201–208 (2004)]. The dependence of the radiation pressure on the acoustic frequency has important consequences including liquid cylinder stabilization. While the radiation pressure is normally associated with sound propagation in the outer gas or liquid, our recent experiments also show that interfacial responses to modulated radiation pressure can be significant when the sound is applied internally to the manipulated object. For example, a liquid jet in air is an acoustic waveguide having a cutoff frequency inversely proportional to the jet diameter. When modulated ultrasound is applied to the jet supply liquid with the ultrasonic carrier frequency near-to or above the cutoff frequency, the jet can be made to oscillate at the modulation frequency of the radiation pressure, thus stimulating jet breakup. [Work supported by NASA.]